Nowadays, due to the growth of the wireless communication industry, a mobile communication system has evolved into a system that can provide a mobile terminal with multimedia communication for transmitting/receiving relatively high-capacity data, such as packet data and multimedia data, as well as voice services.
Furthermore, in the multimedia communication, there is a tendency toward a higher traffic increase in downlink where data/signals are transmitted from a base station to a mobile terminal than in uplink where data/signals are transmitted from a mobile terminal to a base station.
In supporting systems for the multimedia communication, a time division duplex (hereinafter referred to as “TDD”) scheme in which uplink and downlink are divided by time slots is more efficient than a frequency division duplex (hereinafter referred to as “FDD”) scheme in which uplink and downlink are divided by frequencies.
A typical example of the FDD scheme is the IS-95A system or the IS-95B system using code division multiple access (hereinafter referred to as “CDMA”), and a typical example of the TDD scheme is a GSM (Global System for Mobile Communication) communication system using time division multiple access (hereinafter referred to as “TDMA”).
Based on these 2nd generation mobile communication systems, attempts to develop 3rd generation mobile communication systems have been made all over the world. As a result of this, a wideband code division multiple access system and a cdma2000 system based on CDMA have been adopted as the international standard for the FDD scheme.
Also, a time division code division multiple access (hereinafter referred to as “TD-CDMA”) system in which the existing TDMA is extended in such a manner that a plurality of code channels are assigned within a time slot has been adopted as the international standard for the TDD scheme.
The TD-CDMA system includes HCR-TDD (High Chip Rate-TDD) with a chip rate of 3.84 Mcps (cps=chip per second) and LCR-TDD (Low Chip Rate-TDD) with a chip rate of 1.28 Mcps.
The TD-CDMA system can use a maximum of 16 channelisation codes for each time slot. In the TD-CDMA system, a maximum of 16 code channels are used when a spreading gain within one time slot is 16, and less than 16 code channels are used when the spreading gain is less than 16.
In the existing CDMA system based on TDD, for example, in TD-SCDMA, signal detection performance has been enhanced using a type of multiple user detection scheme called joint channel estimation and joint detection.
In particular, DTX (Discontinuous Transmission) is used when ON and OFF intervals are repeated, as in the case of voice, and with regard to this, there has been proposed a method in which joint detection is used only for data of a user who actually transmits data. In this method, a midamble part for channel estimation is always transmitted regardless of whether a receiver is turned on or off, and only whether or not to transmit a data transmission part is determined according to ON/OFF states of the receiver.
Consequently, it is possible to reduce interference regarding the data transmission part, but there is a problem in that channel estimation is still affected by interference regarding the midamble part because the midamble part is transmitted, even when the receiver is turned off.